RNA Polymerase I Inhibition with CX-5461 as a Novel Therapeutic Strategy to Target MYC in Multiple Myeloma

Br J Haematol. 2017 Apr;177(1):80-94. doi: 10.1111/bjh.14525.


Dysregulation of MYC is frequently implicated in both early and late myeloma progression events, yet its therapeutic targeting has remained a challenge. Among key MYC downstream targets is ribosomal biogenesis, enabling increases in protein translational capacity necessary to support the growth and self-renewal programmes of malignant cells. We therefore explored the selective targeting of ribosomal biogenesis with the small molecule RNA polymerase (pol) I inhibitor CX-5461 in myeloma. CX-5461 induced significant growth inhibition in wild-type (WT) and mutant TP53 myeloma cell lines and primary samples, in association with increases in downstream markers of apoptosis. Moreover, Pol I inhibition overcame adhesion-mediated drug resistance and resistance to conventional and novel agents. To probe the TP53-independent mechanisms of CX-5461, gene expression profiling was performed on isogenic TP53 WT and knockout cell lines and revealed reduction of MYC downstream targets. Mechanistic studies confirmed that CX-5461 rapidly suppressed both MYC protein and MYC mRNA levels. The latter was associated with an increased binding of the RNA-induced silencing complex (RISC) subunits TARBP2 and AGO2, the ribosomal protein RPL5, and MYC mRNA, resulting in increased MYC transcript degradation. Collectively, these studies provide a rationale for the clinical translation of CX-5461 as a novel therapeutic approach to target MYC in myeloma.

Keywords: multiple myeloma; myeloma cell lines; myeloma therapy; oncogenes.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents / pharmacology*
  • Antineoplastic Agents / therapeutic use
  • Benzothiazoles / pharmacology*
  • Benzothiazoles / therapeutic use
  • Cell Line, Tumor
  • Disease Models, Animal
  • Drug Resistance, Neoplasm / genetics
  • Gene Expression
  • Gene Expression Profiling
  • Humans
  • Mice
  • Molecular Targeted Therapy
  • Multiple Myeloma / drug therapy
  • Multiple Myeloma / genetics*
  • Multiple Myeloma / metabolism*
  • Multiple Myeloma / pathology
  • Mutation
  • Naphthyridines / pharmacology*
  • Naphthyridines / therapeutic use
  • Proto-Oncogene Proteins c-myc / genetics*
  • Proto-Oncogene Proteins c-myc / metabolism
  • RNA Polymerase I / antagonists & inhibitors*
  • RNA Polymerase I / metabolism
  • Tumor Burden / drug effects
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism
  • Xenograft Model Antitumor Assays


  • Antineoplastic Agents
  • Benzothiazoles
  • CX 5461
  • Naphthyridines
  • Proto-Oncogene Proteins c-myc
  • Tumor Suppressor Protein p53
  • RNA Polymerase I